1. Field of the Invention
The present invention relates to an imaging lens system to be used in various imaging apparatuses using an imaging device such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor), for example, an onboard camera and a monitoring camera, and more particularly to an imaging lens and an imaging apparatus which are suitable for an onboard camera for imaging a video in a front, side or rear part of a car.
2. Description of Related Art
In recent years, an imaging device such as a CCD or a CMOS has greatly progressed a reduction in sizes and an enhancement in a pixel. For this reason, it has also been demanded to reduce a size and a weight for an imaging apparatus body and a lens to be loaded thereon. On the other hand, an onboard camera or a monitoring camera is required to have a high resistance to climate, for example and to be capable of being used within a wide temperature range from an inner part of a car in a tropical area in midsummer to outside air in a cold district, and also is required to have a small size and a high performance. In particular, it has been demanded that a camera disposed in an inner part of a car and serving to monitor a forward part can be used in a wide waveband from a visible range to a near infrared region. JP-A-2006-64829, JP-A-2006-91715 and JP-A-2006-91718 have disclosed a telephoto lens system of a 4-group configuration including a first lens group having a positive power, a second lens group having a positive or negative power, a third lens group having a negative power, and a fourth lens group having a positive power in order from an object side, which can be used in the waveband from the visible range to the near infrared region. In the lens systems described in JP-A-2006-64829, JP-A-2006-91715 and JP-A-2006-91718, a lens in the most object side of the second lens group has a convex surface on the object side. A stop is disposed between the third and fourth lens groups.
In addition to the performance above, in the case where the lens is particularly used as an onboard camera, it is also demanded that a lens portion exposed to an outside is small in order to protect an appearance of a car at the same time. In the lens systems described in JP-A-2006-64829, JP-A-2006-91715 and JP-A-2006-91718, the first lens group has a large diameter and has an insufficiency of a reduction in a size.